Borehole fluid excluder releasably coupled to borehole tool



March 11, 1969 R. L. CALDWELL 3,432,667

BOREHOLE FLUID EXCLUDER RELEASABLY COUPLED To BOREHOLE TOOL Filed April 12, 1965 INVENTOR. RICHARD L. CALDWELL doLJtW,

ATTORNEY United States Patent Oflice 3,432,667 BOREHOLE FLUID EXCLUDER RELEASABLY COUPLED T BOREHOLE TOOL Richard L. Caldwell, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Apr. 12, 1965, Ser. No. 447,263 U.S. Cl. 250-108 5 Claims Int. Cl. GZlf 5/00, 7/00, 9/00 ABSTRACT OF THE DISCLOSURE The specification discloses a borehole fluid excluder releasably coupled to a borehole tool to allow the tool to be retrieved from the borehole in the event the excluder becomes lodged therein. In the emobdiment disclosed, the fluid excluding system is supported by a lower member which is coupled to the tool by shear pins. In the event the excluder becomes lodged in the borehole, an upward force on the tool causes the pins to break, thereby allowing the tool to be pulled through the excluder and out of the borehole.

This invention relates to a borehole fluid excluder for use around a well logging tool and more particularly to a borehole fluid excluder which may be detached from the tool to allow the tool to be retrieved from the borehole in the event the excluder becomes lodged therein.

In well logging operations, borehole liquid affects the measurements desired in that it reduces the sensitivity of the measurements to formation properties. This is particularly true in radioactive well logging operations employing neutrons. It has been found that the effect of the borehole fluid may be reduced by employing excluding means around the exploratory tool to fill substantially the space between the tool and the borehole whereby substantially all of the fluid between the tool and the borehole wall may be displaced. In practical applications, however, such an excluding means may easily become lodged in the borehole thereby making it diflicult to retrieve the logging tool from the borehole.

In accordance with the present invention, there is provided a borehole fluid excluding system which will readily allow the exploratory tool to be retrieved in the event the excluding means becomes lodged in the borehole. The excluding system comprises a means having a low absorption coeflicient for radiation energy employed in the exploratory operation. The excluding means is employed for surrounding the tool, at least around a zone containing exploratory means wherein radiation energy passes between the tool and the formations, and has dimensions whereby it substantially fills the space between the tool and the borehole wall. Coupling means is provided for releasably attaching the excluding means to the tool. The coupling means at least allows the tool to be detached from the excluding means and to be moved upwardly out of the borehole in the event the excluding means becomes lodged in the borehole.

In a more specific aspect, the coupling means allows the tool to become detached from the excluding means upon application of an upward force of a predetermined amount to the tool. In the embodiment disclosed, the coupling means comprises supporting means located below the excluding means for supporting the excluding means and having shear means coupling the supporting means to the tool. In the event the excluding means becomes lodged in the borehole, continued upward force applied to the borehole tool will cause the shear means to break whereby the borehole tool may be withdrawn through the excluding means and out of the borehole.

In a preferred embodiment, the excluding means is 3,432,667 Patented Mar. 11, 1969 utilized with a radioactive well logging tool employing neutrons for exploratory operations. In this embodiment, the excluding means is of solid graphite which is relatively transparent to both fast and slow neutrons as well as to gamma rays. Solid graphite also has advantages for use as a borehole excluder in that it is relatively fragile and hence may be cleared from the borehole passageway, when lodged therein, by simple drilling operations carried out after the tool has been detached from the excluder and removed from the borehole. In addition, the solid graphite is unaffected by high fluid pressures encountered in deep wells.

For further objects and advantages of the present invention and for a more complete understanding thereof, reference now may be had to the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 represents a borehole tool employing the borehole fluid excluding system of the present invention;

FIGURE 2 is an enlarged showing of the system of FIGURE 1 illustrating the manner in which the excluding means is attached to the borehole tool; and

FIGURE 3 is a cross section of FIGURE 2 taken along the lines 3-3 thereof.

Referring now to FIGURE 1 of the drawings, there is illustrated a borehole exploratory tool 10 supported by a cable 11 and employed for investigating the formations traversed by a borehole 12. As shown, the borehole 12 contains borehole liquid 13. The tool 10 contains exploratory means including an energy source 14 for directing radiation energy into the formations and a radiation detector 15 for detecting radiation passing from the formations into the borehole. In applications wherein logging operations are carried out in boreholes cased with iron casing, illustrated at 16, the source 14 preferably is a source of neutrons and the detector 15 is either a gamma ray detector or a neutron detector. It is thus desirable to reduce the effects of the borehole liquid as much as possible. This is accomplished by providing a fluid excluder, illustrated at 17, which surrounds the tool 10 and hence displaces much of the liquid between the tool 10 and the borehole wall. Preferably, the excluder surrounds the tool, at least around the zone containing the neutron source, and, in addition, may also surround the zone containing the detector. The excluding means has a low absorption cross section or coefiicient at least for neutrons and comprises a plurality of solid graphite cylinders. These cylinders are slidably positioned around the tool 10 and are supported by a releasable coupling arrangement comprising a lower supporting means 18 and an upper coupling means 19. The lower supporting means 18 is coupled to the tool 10 by way of a plurality of shear pins, one of which is illustrated at 20. The shear pin attaching arrangement is of special importance in the present system in that it allows the tool to be retrieved in the event the borehole fluid excluder 17 becomes lodged in the borehole. More particularly, in the event the borehole fluid excluder becomes lodged, an upward force upon the logging cable 11 will cause the pins 20 to shear or break. When this occurs, the support 18 will be released and will be free to slide relative to the tool 10. Thus, the tool 10 may be drawn through the borehole fluid excluder 17 and retrieved from the borehole. The graphite excluder 16 may then be cleared from the borehole passageway by drilling operations.

Reference may be had to FIGURES 2 and 3 for a detailed illustration of the shear pin connecting arrangement. Like elements have been given like reference characters as those employed in FIGURE 1.

As illustrated, the supporting means 18 comprises a metal ring slidably positioned around the tool 10 and supported by a second metal ring '21. Ring 21, in turn, is coupled to a third ring 22 by three shear pins 20, as illustrated in FIGURE 3. Ring 22 is securely attached to the borehole tool by cup-shaped member 23, which is threadedly attached to the lower end portion of the tool 10. In the event the excluder 17 becomes lodged in the borehole, upward force to the tool will cause a shearing action or force on the shear pins 20 at the juncture of rings 21 and 22. After a predetermined upward force is applied, the pins 20 will shear or break thereby allowing ring 22 to move relative to ring 21. Further upward force thus will allow the tool 10 to be moved upward relative to rings 21 and 18 and the borehole excluder 17 comprising the plurality of graphite cylinders.

The upward coupling arrangement 19 comprises sleeves 30 and 31. A plurality of nylon set screws, one of which is illustrated at 32, secures the sleeve 30 to the tool 10.

In one embodiment, the sleeves comprising the fluid excluder were obtained from US. Graphite Company, Saginaw, Mich. The material of the sleeves consisted substantially of graphite and is identified as Graphitar grade 80. Each graphite sleeve comprising the eXcluder 17 has an outside diameter of 4.25 inches, an inside diameter of 3.38 inches, and a length of 8 inches. The outside diameter of the borehole tool 10 is such that the graphite sleeves are slidable around the tool. With the upper set screw coupling arrangement, the number of graphite sleeves employed may be varied. The excluder arrangement disclosed is capable for use in boreholes having an inside diameter one-fourth of an inch greater than the outside diameter of excluder 17. The outside diameter of the ring 18 is the same as that of the graphite sleeves forming the excluder 17. The supporting rings 21 and 22 were of stainless steel having a thickness of threeeighths of an inch. The outside diameter of ring 22 and hence the inside diameter of ring 21 was about 3.25 inches. The outside diameter of ring 21 was of the order of 3% inches. The shear pins 20 were of stainless steel having a diameter of 0.1 inch and a length of five-eighths of an inch.

In the embodiment shown in FIGURE 1, the borehole cable 11 is wound and unwound upon drum 40 driven by motor 41 and mechanical connection 42. The output of detector is applied to cable conductor 43 for transmission to the surface where signals are taken therefrom by slip ring 44 and brush 45 and applied to a readout 46.

Now that the invention has been described, modifications will become apparent to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.

I claim:

1. A well logging system comprising:

a borehole tool adapted to be inserted into a borehole, said tool having a zone containing energy source and detecting means for investigating the formations traversed by said borehole,

borehole liquid excluding means surrounding said tool for displacing borehole liquid from between said tool and the borehole wall,

said borehole liquid excluding means including:

upper and lower annular members adapted to be coupled to said tool above and below said zone respectively, at least said lower member being a rigid member, shear means releasably coupling at least said lower rigid member to said tool, means including annular liquid displacing means surrounding said tool and located and supported between said upper and lower members for displacing borehole liquid from between said tool and the borehole wall at least around said zone, said annular liquid displacing means presenting less interference than said borehole liquid to the investigation operations to be carried out with said source and detecting means, said annular liquid displacing means having an internal diameter of a size sufficient to allow said tool to be pulled upward through said annular liquid displacing means, said shear means allowing said tool to be detached at least from said lower rigid member upon the application of an upward force of a predetermined amount to said tool in the event said excluding means becomes lodged in said borehole whereby said tool may be pulled upward through said annular liquid displacing means to allow said tool to be pulled upward and out of said borehole. 2. The system of claim 1 wherein: said source is a neutron source and said detecting means is a neutron detector. 3. The system of claim 1 wherein: said source is a neutron source and said detecting means is a gamma ray detector. 4. The system of claim 1 wherein: said source is a neutron source, said excluding means being of graphite. 5. The combination of claim 1 wherein: said borehole tool is employed for radioactive well logging wherein neutrons are employed in exploratory operations, said excluding means having a low absorption coeflicient for neutrons.

References Cited UNITED STATES PATENTS 2,509,908 5/1950 Crumrine.

2,652,496 9/1953 Herzog et a1.

2,747,100 5/ 1956 Wyllie et al. 250108 X 3,065,346 11/1962 Dewar et al 250108 X 3,097,696 7/1963 Orr 166-123 X 3,211,230 10/1965 Stone 166-123 X 3,288,210 11/1966 Bryant 166-35 X 3,294,171 12/1966 Kelley 166123 X RALPH G. NILSON, Primary Examiner.

SAUL ELBAUM, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,432,667 March ll, 1969 Richard L. Caldwell It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 15, "emobdiment" should read embodiment line 48, operation should read operations Column 4, lines 1 to 7 should appear in the following form:

said borehold liquid excluding means including:

upper and lower annular members adapted to be coupled to said tool above and below said zone respectively,

at least said lower member being a rigid member,

shear means releasably coupling at least said lower rigid member to said tool,

Column 4, line 51, "Dewar et al. should read Dewan et a1. line 53 "Stone" should read Stone, Jr.

Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. WIEJLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

